The invention is directed to a blue glass composition and method of producing; a blue glass with an improved infrared absorption.
It would be extremely advantageous to improve the infrared absorption of glass products while maintaining a high level of visible transmission and to also have a good absorption in the ultraviolet portion of the spectrum. As is well known in the art, iron oxide is commonly used to provide a green color to glass. Iron oxide exists in two chemical forms in the glass, an oxidized form which is yellow: Fe2O3, and a reduced form which is blue FeO. Advantageously, the oxidized form of iron oxide absorbs a portion of the ultraviolet light passing through the glass product and the reduced form of iron oxide absorbs a portion of the infrared light passing through the glass product. Under typical furnace firing conditions arid batching conditions, when the total iron oxide in the glass product is within the range of about 0.3 to 0.8 wt. % as Fe2O3, the iron oxide equilibrium is such that the redox ratio of FeO/total Fe as Fe2O3 is about 0.23-0.26.
It is desirable to increase the proportion of reduced iron oxide (FeO) in the glass to improve its infrared absorption. In addition, by shifting the iron oxide away from the oxidized form (Fe2O3) the glass will change color from green to blue. The total iron oxide concentration may be decreased to maintain a high visible transmittance of the glass as the reduced iron absorbs more in the visible portion of the spectrum than the oxidized iron.
One way commonly employed to shift the redox equilibrium of iron oxide in the glass, and hence its UV and IR properties, is by increasing the fuel to the furnace. Increasing the amount of fuel, however, has several undesirable consequences: the combustion heating of the furnace becomes inefficient and requires an air increase or the unburnt fuel will burn in the checker system of the furnace. Excess fuel can also reduce the glass to an amber color that sharply lowers the visible transmittance of the glass product.
An amber color arises when the iron reacts with sulfur that has been reduced to form iron sulfide. Amber colored glass containers are normally melted in like manner by using anthracite coal together with iron oxide and sulfate. The amber iron sulfide chromophore, once produced, significantly decreases the visible transmittance of the glass and the glass could not be used where a high transmittance is required.
Therefore, there is a need in the glass industry to produce amber free blue glass that has high transmittance yet having an improved infrared light absorption and an ultra violet absorption.
The present invention is a blue soda-lime-silica glass composition that is heat absorbing. The composition comprises 68 to 75% SiO2, 10 to 18% Na2O, 5 to 15% CaO, 0 to 10% MgO, 0 to 5% Al2O3, and 0 to 5% K2O, where CaO+MgO is 6 to 15% and Na2O+K2O is 10 to 20%, and colorants consisting essentially of: 0.3 to 0.8 wt. % total iron oxide as Fe2O3 wherein the ratio of FeO/total Fe as Fe2O3 is greater than 0.35 but less than 0.62; 0.05 to 0.5 wt. % manganese compound as MnO2; 0 to 0.30 wt. % titanium oxide as TiO2, and 0 to 0.8 wt. % cerium oxide as CeO2.
Glass products made according to the embodiment of the invention have the following spectral properties at 4.0 mm. Thickness 65 to 81% light transmittance using Illuminant A (LTA) and using Illuminant C has a dominant wavelength greater than 488 but less than or equal to 494 nanometers with an excitation purity greater than 4 and less than 11%. Generally, as the quantities of the colorants increase, both the % LTA and % IR transmittance will go down. Similarly, as the glass thickness increases for a given glass composition, the transmittance of the thicker glass will decrease.
Flat soda-lime-silica glass, used in the automotive and architectural industries and conveniently made by the float glass process, is generally characterized by the following basic composition, the amounts of the components being based on a weight percentage of the total glass composition:
The blue glass composition of the present invention employs this basic soda-lime-silica glass composition wherein, additionally, CaO+MgO is 6 to 15 wt. % and Na2O+K2O is 10 to 20 wt. %. Preferably SO3 is 0.02 to 0.20 wt. %, more preferably 0.02 to 0.10 wt. %. In addition, the blue glass composition consists essentially of the following coloring components: iron oxide; manganese compound; and optionally any of titanium dioxide or cerium oxide or both.
The total iron oxide as Fe2O3 present in the invention composition in quantities of 0.3 to 0.8 wt. % Fe2O3. Typically, this ingredient is added with the batch ingredients in the oxide form, Fe2O3. The iron oxide incorporated in the composition lowers both the ultraviolet and the infrared transmittance of the glass products. When iron is used in a glass composition in normal commercial production, the redox ratio defined as equal to FeO/total Fe as Fe2O3is 0.23-0.26, while glass of the invention has a higher redox ratio of 0.35-0.62. If the redox ratio goes above 0.62, the undesirable amber chromophore may form.
The most important factor of glass of the invention is the one step batch admixing of the components to feed a conventional siemens float glass furnace. Sodium sulfate is mixed in the batch together with anthracite coal to shift the iron oxide equilibrium toward the reduced form of iron. Manganese dioxide is necessary in the batch to prevent the formation of the amber iron sulfide. All of the batch components are mixed together in a single step and then metered into the furnace. The glass product made with this method becomes blue and the infrared absorption of the product is measurably improved. When glass products made in this manner are used in vehicles, the blue glass absorbs solar heat and there is less total heat build up in the vehicle. The load on vehicle air conditioners is reduced such that there is less heat build up to cool and comfort to the passengers occurs quickly. Glass made with the instant invention can also be used for architectural products and provides a similar reduction in air conditioner load.
A manganese compound is present in an amount of 0.05 to 0.5 wt.% based on MnO2 in the blue glass invention composition to prevent the formation of the amber color. This manganese compound can be added to the batch glass components in a variety forms, e.g., but not limited to MnO2, Mn3O4, MnO, MnCO3, MnSO4, MnF2, MnCl2, etc.
Table II discloses the amounts of raw material batch ingredients that are preferably used to form the embodiments of blue glass compositions according to the present invention.
CARBOCITE is anthracite coal from the Shamokin Filler Company. Graphite could be used as a substitute for anthracite coal in an amount of about 70% that of anthracite coal because anthracite coal contains about 70-72% carbon, the typical range would be from 0.7 to 2.1 pounds of graphite per 1000 pounds of sand. MELITE, a coal slag processed by Calumite Corporation could partially or wholly substitute for rouge in the batch up to about 55 pounds Melite per 1000 pounds of sand. MELITE has about 80% of the total iron oxide in the reduced form and thus would require less anthracite coal to generate similar spectral properties.
The equilibrium reactions that occur in the glass melt which cause a shift in the forms of iron oxide are included by the sodium sulfate used as a refining agent and carbon used to react with sodium sulfate at lower furnace temperatures. Generally, increasing the quantity of sodium sulfate in the glass tends to shift the iron oxide equilibrium slightly toward oxidizing while increasing carbon concentration in the glass batch shifts the iron oxide equilibrium toward reducing. Another influence on the iron oxide equilibrium is the peak furnace temperature which when increased will shift the iron oxide slightly toward the reduced state and lowering overall furnace temperature allows the iron oxide to shift toward the oxidized state.
Melts were made in the laboratory which demonstrate embodiments of this invention using the procedure as follows: 2xe2x80x3 inside diameter and dry mixed for 10 minutes each on a Turbula mixer, dry batch was placed into an 80% platinum 20% rhodium crucible that stands 2xe2x80x3 tall and has an inside diameter at the top of 2.5xe2x80x3 and is tapered to the base which has an inside diameter of 1.75xe2x80x3. An amount of 4.5 ml. of water is added to the dry batch in the crucible and mixed with a metal spoon. After such preparation, a group of six different batches is melted in a gas/air fired surface at the same time for 1 hour at 2600xc2x0 F. and each crucible is removed in turn from the furnace and fritted. Fritting the glass involves coating the inside of the platinum/rhodium crucible by rolling the molten, glass around the inside of the crucible and then plunging the crucible into cold water. After removing, the crucible from the water and draining, the broken glass particles are removed from the sides of the crucible and mechanically mixed inside the crucible. All six samples are fritted in like manner and all crucibles are placed back into the furnace for another hour interval at 2600xc2x0 F. and the fritting procedure is repeated. After the second fritting process, the crucibles are returned to the furnace for 4 hours at 2600xc2x0 F. Each crucible is removed in turn from the furnace and each molten glass sample is poured into a graphite mold with an inside diameter of 2.5xe2x80x3. Each glass is cooled slowly, labeled, and placed into an annealing furnace where the temperature is quickly raised to 1050xc2x0 F., held for 2 hours, and then slowly cooled by shutting off the furnace and removing the samples after 14 or more hours. The samples are ground and polished to about 4.0 mm. thickness and subsequently the spectral properties are measured for each sample.
All of the examples are made using the above batch only with no cullet (the broken pieces of glass that are added to the batch feed in production). There are two types of cullet that can be added to the batch to produce glass of the invention: reduced iron blue glass from glass of the invention and oxidized iron green glass. The reduced iron blue glass cullet has a redox ratio of about, 0.5 to 0.6 while the oxidized iron green glass has a redox ratio of about 0.25. The redox ratio is defined as the ratio of wt. % FeO/total Fe as wt. % Fe2O3. For example, if the desired glass of the invention uses 2 pounds of anthracite coal for 1000 pounds of sand, then an additional 1.5 pounds of anthracite coal must be added to the batch when the reduced iron blue glass cullet is added to make 50% of the batch feed to the furnace for a total of 3.5 pounds of anthracite coal per 1000 pounds of sand. For other cullet levels, the anthracite coal is increased or decreased proportionately. If the oxidized iron green glass cullet is used, more anthracite coal must be added to drive the oxidized cullet toward the reduced iron blue color. For example, if the desired glass of the invention uses 2 pounds of anthracite coal for 1000 pounds of sand, then an additional 2.5 pounds of anthracite coal must be added to the batch when the oxidized iron green glass cullet is added to make 50% of the batch feed to the furnace for a total of 4.5 pounds of anthracite coal per 1000 pounds of sand. When other reductants are used, they must be adjusted proportionately as the anthracite coal in the examples.
All laboratory melts made with above procedure use a base composition of 100 grams sand, 32.22 grams soda ash, 8.81 grams limestone, 23.09 grams dolomite, 0.5 to 2.0 grams of sodium sulfate, 0.1 to 0.25 grams of CARBOCITE, 2.64 grams of nepheline syenite, and the remainder of the batch includes rouge, manganese dioxide, and titanium dioxide and cerium oxide, if required.
In each of the following tables of examples with the glass composition includes spectral data at 4.0 mm., which is the control thickness. Some tables include thickness other than 4.0 mm. where the most preferred embodiment of the instant invention is with the % LTA greater than or equal to 70.0% and the TSET is less than or equal to 40.0%.